The present invention relates to a fuel injector.
Fuel injectors which are provided with a disk with fuel channels for guiding a valve-closure member and for generating a swirl in the fuel flow are described in German Patent Application No. DE 36 43 523. The fuel channels have a tangential component, which imparts a circumferential component to the velocity vector of the flow. The flow cross-section, which is open across the entire cross-section of the fuel channel, has a restricting effect on the flow rate. Throttling the flow causes a pressure decrease at the disk, which is utilized to form a sealing surface pressure and to avoid a secondary flow path. Fuel metering and swirl generation occur upstream from the sealing seat. With the aid of a bore introduced in the center of the disk, the valve-closure member, and the valve needle, respectively, are also radially guided, the tolerance of the gap formed between the valve needle, or the valve-closure member, being chosen so as to obtain an hydraulically sealing fit.
Another fuel injector is described in German Patent Application No. DE 196 25 059, where the metering of the fuel quantity and the formation of a swirl-imparted flow also occur upstream from the sealing seat. In this case, the fuel channels, which are used to meter the fuel, are designed either as bores or as grooves, the grooves being closed by the valve-seat surface to form swirl channels.
Both of the above-described fuel injectors have fuel channels whose cross-section determines the metering of a specific fuel quantity. Simultaneously, the tangential components of the fuel channels produce a swirl in the fuel flow. Observing tight tolerances when introducing the flow channels is thus of paramount importance for the precise metering of the fuel quantity to be injected. This makes the manufacture expensive, which is a disadvantage.
Another disadvantage of the mentioned fuel injectors is the strong response to contamination of the channels. A modification of the cross-section as a result of contaminated channels causes a change in the metered quantity and, due to the swirl generation, a change in the jet angle as well.
Moreover, the possible deposition of dirt particles contained in the fuel in the area of the valve-sealing seat is also disadvantageous. Deposits formed in the area of the valve-sealing seat prevent a complete closing of the fuel injector and, in this way, may allow the escape of a small quantity of fuel after the spray-off process has been concluded. A degraded mixture formation and combustion are the result.
A fuel injector according to an example embodiment of the present invention, may have the advantage that dirt particles that are carried through the swirl channels by the fuel flow have no opportunity to settle along the further flow route. The swirl channels constitute the narrowest dimension of the flow route to the spray-off orifice, so that a contamination of the sealing seat is prevented.
The small diameter of the individual swirl channels acts as a filter for any dirt particles present in the fuel flow. The dirt particles are filtered out at the upstream side of the swirl disk.
Also advantageous is the minimal effect a contamination of individual swirl channels has on the swirl formation. The clogging that may occur at the upstream side of the swirl disk by filtering out dirt particles that are carried along, reduces the entire unobstructed flow cross-section only to a minimal extent. The effect on the swirl generation is negligible.